The present invention relates to laboratory equipment, commonly referred to as “tissue recording chambers” or “brain slice chambers” which allow the user to record and assess the effects of drugs and toxins on living, electrically excitable tissues.
Apparatus of this type are often used to analyse the effects of drugs and/or neurotoxins on brain tissue from rats. However, recording techniques have been recently adapted to include cardiac tissue. Other excitable tissues of potential interest are skeletal muscle and retina.
In an example of a tissue recording system of the prior art, fluids are directed into a chamber through a small diameter stainless steel tube which projects into a tissue recording chamber, also known as a slice bath. The fluids contain oxygen, salts and essential nutrients for the tissue, as well the toxins or drugs which are the object of the study.
The subject tissue slice is held in position between two nets. Fluids superfuse the tissue and then flow into a reservoir or moat or which directs the fluids out again through a separate channel and into a suction port. The fluids are drawn out of the suction port by a disposable small gauge needle fitted to an adjustable post which allows the user to regulate the level of the fluid in the suction port, and therefore in the recording chamber. The fluids are finally drawn away from the tissue recording system via a length of flexible tubing which extends between the needle and a vacuum source.
An electrical stimulus is applied to the tissue slice via an electrode connected to a micromanipulator. The signal produced by the tissue sample is recorded by a second electrode held in a second micromanipulator. An amplifier is provided in the base of the micromanipulator to amplify the signal before it is recorded by a data recording system.
The prior art apparatus described above has a number of inherent disadvantages.
Electrical grounding and communication of the recording chamber ‘bath potential’ to the amplifier is achieved by a small spring loaded pin which is pressed into the underside of the recording chamber to make contact with a stainless steel fluid input tube. The pin also makes contact with the upper surface of an annular grounding ring pressed into the recording chamber platform. The upper surface of the grounding ring is also in contact with a spring loaded pin which is in direct contact with an amplifier housed in the base of the micromanipulator.
This system of grounding works reasonably well in terms of grounding noise entering the system via the input tube, but may fail to adequately ground noise entering the system through the vacuum line and suction port. In addition, the spring loaded pins may be physically weak and prone to failure following several years of use.
Recording and stimulating electrodes are positioned over the tissue slice using modular attachable micromanipulators which are designed to hold adjustable tubular steel electrode guides. The guides hold fixed electrodes. The electrode pin sockets are permanently affixed in plastic end caps and the user then manually connects the electrodes for use on a daily basis.
The tubular steel probe guides are gripped in the ‘arms’ of the micromanipulators and can be slid up or down as needed to allow the micromanipulator arm to be swung aside for placement of fresh slices in the bath. However, the extremely delicate electrodes themselves are in danger of damage, and the probe guides can not be removed for storage without first removing the individual electrodes.
The tissue sample is held in position in the bath between two net rings. The two rings fit together, one within the other, and are referred to as the top net and the bottom net. Together they serve to sandwich and stabilize tissue slices for vibration-free recording.
The nets are relative fragile. If the nets are torn during use, which is reasonably common, then the user has to sand away and manually replace the netting material. With repeated use the net rings tended to lose their original fit, becoming too tight, and requiring sanding or honing, or too loose, requiring the fabrication of spacers or shims to prevent slippage. Because they often fit very snugly in the bath and to one another, and because they are small and difficult to grip, a special tool is required to remove the net rings.